krhplatform.h currently contains:
/*
* Types that are (so far) the same on all platforms
*/
typedef signed char khronos_int8_t;
typedef unsigned char khronos_uint8_t;
typedef signed short int khronos_int16_t;
typedef unsigned short int khronos_uint16_t;
typedef signed long int khronos_intptr_t;
typedef unsigned long int khronos_uintptr_t;
typedef signed long int khronos_ssize_t;
typedef unsigned long int khronos_usize_t;
However, 64bit Windows uses an LLP64 model¹, where longs are 32bits and pointers are 64bits.
Thus the definitions khronos_{u,}intptr_t and khronos_{s,u}size_t need to be specialised.
For the C99 case this could just be to typedef the existing {u,}intptr_t, and for POSIX at least to typedef ssize_t to khronos_ssize_t and size_t to khronos_usize_t.
1: http://technet.microsoft.com/en-us/library/bb496995.aspx